1. Field of the Invention
The present invention relates to a multi-laminated inductor used for various circuits and a manufacturing method and more particularly to a multi-laminated inductor comprised of laminated internal conductors forming a coil along the length of the chip.
2. Description of the Related Art
Conventional multi-laminated inductors are classified into two broad categories in the relation between the direction of laminating internal conductors and the outside shape of the chip, which form the coil. For example, multi-laminated chip inductors have such a structure that coil-shaped internal conductors made of silver or silver-palladium alloy are contained in a nonconductor material or ferrite magnetic material and both ends of the coil are connected to external terminal conductors respectively.
FIG. 2 shows a relation between the direction of laminating internal conductors and the outside shape of the chip in this multi-laminated chip inductors. It has one structure that the internal conductors 2 are laminated along the thickness Lt (or width Lw) of the multi-laminated chip inductor 1. Usual multi-laminated chip inductors have this structure. Here, the both ends of a coil-shaped conductor are connected to external terminal conductors 3a and 3b, respectively.
On the other hand, Japanese Patent Application Laid-Open No. 8-55726 teaches the another structure of a multi-laminated chip inductor 6 as shown in FIG. 3. That is, internal conductors 4 are laminated along the length L1 of the chip 6 and are external terminal conductors 5a and 5b formed at both end portions along its length.
This structure is generally referred to as a longitudinal stack type, and has features that it can provide relatively high inductance values and high self-resonance frequencies.
A multi-laminated chip inductor of the longitudinal stack type has a laminated structure as shown in FIG. 4, for example. That is, a coil is formed by laminating a plurality of magnetic material sheets 7a and 7b having internal conductor patterns 4a and 4b shaped like a letter L thereon, and then connecting the internal conductors 4a and 4b through via holes 8a and 8b into the shape of a spiral. Further, both ends of the coil formed by the internal conductor patterns 4a and 4b are connected to via holes 8c and 8d formed in a plurality of laminated magnetic material sheets 7c and 7d, respectively.
Thereby, lead conductor portions are formed by coupling a plurality of via holes 8c and 8d. The via holes 8c and 8d exposed to the surfaces of the magnetic material sheets 7c and 7d placed at both ends are connected to the external terminal electrodes 5a and 5b. These external terminal conductors 5a and 5b are formed on the both end faces along the length of the chip and on portions of the faces adjacent to these end faces.
In the conventional multi-laminated chip inductors 6 of the longitudinal stack type described above, the external terminal electrodes 5a and 5b are formed on both end faces along the chip length in which are perpendicular to the winding center-line of the coil formed by internal conductors 4.
Therefore, when the magnetic flux generated by the passage of electric current through the coil passes through the external terminal electrodes 5a and 5b, eddy current is generated within the external terminal electrodes 5a and 5b. This eddy current has been one of the factors that increase its electrical loss.
Further, as the internal conductors 4 and the external terminal electrodes 5a and 5b are disposed nearly parallel to each other, stray capacity is produced between them. This stray capacity has been one of the factors behind a reduction in the self-resonance frequency of the inductors.
Also, in manufacturing of multi-laminated chip inductors of the longitudinal stack type described above, there has been no approach for adjusting a value of inductance except re-designs such as changing the core area. It has been also necessary to change the content of design for each different value of inductance. Thus, the control of design specification has been very complex.